Smith-Lemli-Opitz syndrome (SLOS) is a dysmorphology and mental retardation disorder lacking adequate therapy options. It is caused by cholesterol deficiency due to inactivity of 7-dehydrocholesterol-delta7-reductase (DHCR7). Biochemically, it is characterized by low concentrations of cholesterol (C) in blood and tissues and high concentrations of dehydrocholesterol (DHC). Although mutations in the DHCR7 gene have been well described, the pathogenic development of the disease characteristics is not well understood. Among inherited errors of metabolism, SLOS is relatively frequent, and new diagnostic methods aid its prenatal detection. The long-term objective of this proposal is to develop a basis for the treatment of SLOS. For experiments, mouse models that closely mimic human SLOS will be used. Three Specific Aims are proposed: (Aim 1) Identify and quantify biochemical markers of SLOS. Using highly sensitive mass spectrometric methods, sterols and steroids will be measured in serum, urine and tissues of mutant and control mice. Ratios of DHC/C and dehydro steroids/normal analogs will provide markers for evaluating mutant severity, biochemical changes during development and effects of treatments. Because major characteristics of SLOS include neurological problems, special attention is given to neurosteroids. (Aim 2) Normalize cholesterol levels in adults and newborns. The effects of dietary cholesterol and gene transfer will be evaluated using the biochemical markers. Gene transfer experiments will utilize viral vectors to deliver a functional DHCR7 gene to the mutant mice. Because SLOS is both a developmental problem and a continuing problem perpetuated by deficient cholesterol metabolism, mice will be treated at different developmental stages. This will help establish the time line of pathogenesis and aid distinguishing between irreversible (untreatable) and reversible (treatable) SLOS characteristics. Aim 3. Correct cholesterol levels during fetal development. Here the emphasis is on preventive treatment and establishing when during development irreversible damage occurs. Both biochemical markers and dysmorphic features will be monitored. Later tests for all three Specific Aims will explore neuromuscular and behavioral performance to see if they are correlated with changes in the biochemical markers. Long-term consequences, safety and potential adverse effects of treatment will also be monitored. Because of the multiple essential roles of cholesterol, SLOS is a complicated and devastating disease in spite of its relatively simple genetic origin. The frequency of SLOS in North America is estimated to be in the range of 1 in 20,000 to 30,000, although many cases are thought to be never diagnosed. Through the proposed experiments using SLOS mice, we hope to learn more about the timing and biochemistry of disease development and to establish a basis for eventual treatment in humans.